A conversion problem

30/03/2001
Down To Earth

A conversion problem catalytic converters, meant to clean up car exhausts, are polluting the environment. A group of Italian and French researchers have found traces of heavy metals emitted from the devices in remote regions of Greenland.

Seth Dunn of the Worldwatch Institute, a non-governmental organisation based in Washington dc, usa, says, "They have broken new ground.' He says. "The implications could be significant for public health.' Workers involved in refining platinum, one of the metals used in catalytic converters, are known to suffer a higher than usual incidence of asthma.

"The fact that we found the metals in Greenland means that it's a global problem. It's not just close to the cities or the highways,' says chemist Carlo Barbante of the University of Venice. The us, Canada and Japan had introduced cars with catalytic converters back in the mid-1970s. Europe followed in the early 1990s. In India, they have been made mandatory for vehicles registered in Delhi. In these devices platinum, palladium and rhodium catalyse reactions that convert hydrocarbons, carbon monoxide, and nitrogen oxides into less noxious emissions.

But the study has found that exhausts from fast-moving cars erode catalytic converters, emitting microscopic particles containing the metals (New Scientist, Vol 196, No 2277).

To assess the global impact of these particles, Barbante and his colleagues extracted ice and snow cores in Greenland dating from 1969 to 1988 and from 1991 to 1995. They also took samples, dating back nearly 7500 years, from the Greenland Ice Core Project. They found that metal concentrations in the snow have been rising steadily since 1976. Rhodium levels are already 120 times higher than in the 7,500-year-old ice. Palladium levels have increased 80-fold while the platinum concentration has increased by 40 times. The ratio of platinum to rhodium in the snow from the mid-1990s resembled the ratio in car exhausts. This suggests that most of the increase in platinum and rhodium comes from catalytic converters, says Barbante.

At present concentrations of these metals in urban ambient air are too low to pose a serious health risk. But the metals, especially palladium, can accumulate in plants and animals and enter the food chain. Kym Jarvis, environmental geochemist at Kingston University, uk and her colleagues have discovered that palladium is soluble in a dilute acid solution. "The high solubility of palladium suggests that, once it reaches the road surface, it can be more readily absorbed by vegetation, or which can get into the waterbodies,' she says.

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